Approximately 10% of the population become hypersensitized (allergic) upon exposure to antigens from a variety of environmental sources. Those antigens that induce immediate and/or delayed types of hypersensitivity are known as allergens (King, T. P., (1976) Adv. Immunol., 23: 77–105. These include products of grasses, trees, weeds, animal dander, insects, food, drugs, and chemicals. Genetic predisposition of an individual is believed to play a role in the development of immediate allergenic responses (Young, R. P. et al., (1990) Clin. Sci., 79: 19a) such as atopy and anaphylaxis whose symptoms include hay fever, asthma, and hives.
The antibodies involved in atopic allergy belong primarily to the IgE class of immunoglobulins. IgE binds to basophils, mast cells and dendritic cells via a specific, high-affinity receptor FcεRI (Kinet, J. P., (1990) Curr. Opin. Immunol., 2: 499–505). Upon combination of an allergen acting as a ligand with its cognate receptor IgE, FcεRI bound to the IgE may be cross-linked on the cell surface, resulting in physiological manifestations of the IgE—allergen interaction. These physiological effects include the release of, among other substances, histamine, serotonin, heparin, chemotactic factor(s) for eosinophilic leukocytes and/or leukotrienes C4, D4, and E4, which cause prolonged constriction of bronchial smooth muscle cells (Hood, L. E. et al., Immunology (2nd ed.), The Benjamin/Cumming Publishing Co., Inc. (1984)). Hence, the ultimate consequence of the interaction of an allergen with IgE are allergic symptoms triggered by release of the aforementioned mediators. Such symptoms may be systemic or local in nature, depending on the route of entry of the antigen and the pattern of deposition ofIgE on mast cells or basophils. Local manifestations generally occur on epithelial surfaces at the site of entry of the allergen. Systemic effects Can induce anaphylaxis (anaphylactic shock) which results from IgE-basophil response to circulating (intravascular) antigen.
The pet dog (Canis familiaris) is kept in households the world over. In houses and public schools where dogs have been kept on a regular basis, dog dander allergens can be detected in dust samples (Wood, R. A. et al, (1988) Am Rev Respir. Dis., 137: 358–363, and Dybendal, T. et al., (1989) Allergy, 44: 401–411). The prevalence of allergy to dogs as assessed by skin prick test is approximately 15% (Haahtela, T. et al., (1981) Allergy, 36: 251–256, and de Groot, H. et. al, (1991) J. Allergy Clin. Immunol., 87: 1056–1065). In one study, sensitivity to dog allergen(s) was detected in 40% of asthmatic children, even though dogs were not kept as pets in their homes (Vanto, T. and Koivikko, A., (1983) Acta Paediatr Scand., 72: 571–575).
Treatment of patients with dog allergy by administration of dog dander extracts has not proven to be as efficacious as treatment of cat allergic patients with cat dander extracts (Hedlin, G. et. al., (1991) J. Allergy Clin Immunol., 87: 955–964). As with any desensitization scheme involving injection of increasing doses of allergen(s), there are the drawbacks of potential anaphylaxis during treatment, and the possible necessity of continuing therapy over a period of several years to build up sufficient tolerance that results in significant diminution of clinical symptoms.
Dog hair and dander extracts are complex mixtures containing a number of allergenic proteins. (Loewenstein, H et al., (1982) Proceedings 11th International Congress of Allergology and Clinical Immunology. London, pp 545–548; Uchlin, T et al. (1984) Allergy, 39: 125–133: Yman. L. et. al., (1984) Int. Arch. Allergy Appl. Immunol. U, 44: 358–368; Spitzauer, S. et. al., (1993) Int. Arch. Allergy Immunol., 100: 60–67). Two allergens present in dog hair/dander have been purified using immunoaffinity chromatography. A major allergen from dog, Can fI (Nomenclature according to the criteria of the IUIS (Marsh, D. G. et. al., (1988) Clin. Allergy. 18: 201–209; Agl3 according to original nomenclature), has been partially purified by two groups (Schou, C. et al., (1991) Clin. and Exp. Allergy. 21: 321–328 and de Groot et al., supra). Both groups, partially purified Can fI was established as an allergen by CRIE analysis (Ford A. W. et. al., (1989) Clin. Exp. Allergy. 19: 183–190), and then rabbits or Balb/b mice were immunized to obtain polyclonal or monoclonal antibodies against the allergen, respectively. Immunoaffinity purified Can fI (˜25 kD in molecular weight, with a minor component ˜18 kD) which elicited a high frequency of positive skin prick tests among dog allergic patients was able to deplete 50–70% ofIgE binding to dog dander extracts in RAST (radioallergosorbent test) analysis. While de Groot et. al. did not attempt to determine any amino acid sequence of Can fI. Schou et. al. found the amino terminus of their immunoaffinity purified Can fI was blocked. Hence, no amino acid sequence of Can fI is presently in the public domain.
The presence of a second (minor) allergen in dog extract was detected by binding ofIgE antibodies to dog dander/hair extracts by several groups (de Groot et al., supra. Schou, C. et. al., supra and Spitzauer et. al., (1993) Int. Arch. Allergy Immunol., 100: 60–67). The molecular weight of a minor allergen was reported to be 18 kD (Schou et al., supra), 19 kD (Spitzauer et al., supra) and 27 kd (de Groot et. el., supra). It is difficult however to correlate these results since only one group (de Groot et al., supra) affinity purified an allergen designated Can fII (originally named Dog 2 allergen). Can fII was purified from dog dander extracts in a manner analogous to Can fI using monoclonal antibodies generated to a second allergen present in extracts (de Groot et. al., supra). Molecular weight of Can fII reported by this group as ˜27 kD was later verified to be ˜24 kD (Aalberse, R. C. personal communication). Purified Can fII allergen was found to react with IgE of only 66% of dog allergic patients. In RAST analysis, Can fII allergen was able to compete with 23% of the IgE directed against dog dander extract. The amino acid sequence of Can fII has not been previously determined.
Many patients with sensitivity to dog dander allergens are treated currently by administration of small, gradually increasing doses of dog dander extracts. Use of these extracts has multiple drawbacks, including potential anaphylaxis during treatment and the necessity of continuing therapy, often for a period of several years to build up sufficient tolerance and significant diminution of clinical symptoms. The ability to substitute compositions of at least the major dog dander allergens, such as Can fI and Can fII, would overcome several of these drawbacks. Thus, a source of pure allergen that could be provided in quantity for use as a diagnostic or therapeutic reagent and therapeutic methods that would overcome the drawbacks associated with dog dander extracts are highly desirable.